It has long been known to print documents, to protect them from forgery, using fine patterns constituting a background for a main image. The more complex the fine pattern, the more difficult it is to reproduce.
The developments of xerography, laser printing and scanning have created new problems for the printer. Special measures have been devised to make security documents uncopiable by standard or even advanced state of the art copiers and scanners, EP 0920383 being an example of such in which an “object” is worked into a background pattern by linear components of the background being “hollowed” i.e. thick lines becoming slightly spaced thin lines. Such hollowed regions are not readily visible to the naked eye, so they do not mar the appearance of the major image, but they “fool” a photocopier, and are visible in a photocopy. The object″ in question can be a word, such for example, as “FORGERY”.
This is fine for demoralising the would-be forger who is sophisticated enough only to rely on a photocopier. The first copy taken on the machine appears with the word “FORGERY” in it, and the would-be forger is supposed to abandon the attempt.
The determined forger, however, will realise that he is simply using the wrong copying technique, and switch to something more appropriate.
Essentially, the truth of the mailer is that anything that can be made can be copied, if enough resource is put into the attempt. It is, clearly, only necessary to replicate the production process for the original, and the copy will be perfect. Where there is sufficient incentive, the cost of replicating the production process will be willingly borne by the forger.
There are documents, however, that, while needing to be secure, do not merit undue cost in their creation.